Multiattack

The devil makes two attacks with its fork and one with its tail. It can replace any melee attack with Hurl Flame.

Fork

Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 5) piercing damage plus 3 (1d6) fire damage.

Tail

Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 10 (1d10 + 5) piercing damage. If the target is a creature other than an undead or construct it makes a DC 17 Constitution saving throw. On a failure it receives an infernal wound and takes 11 (2d10) ongoing piercing damage. Each time the devil hits the wounded target with this attack the ongoing damage increases by 11 (2d10). A creature can spend an action to make a DC 12 Medicine check ending the ongoing damage on a success. At least 1 hit point of magical healing also ends the ongoing damage.

Hurl Flame

Ranged Spell Attack: +7 to hit, range 150 ft., one target. Hit: 10 (3d6) fire damage. If the target is an unattended flammable object or a creature it catches fire taking 5 (1d10) ongoing fire damage. A creature can use an action to extinguish this fire.

Inferno (1/Day, While Bloodied)

The devil waves its fork igniting a trail of roaring flame. Any creature within 10 feet of the devil makes a DC 15 Dexterity saving throw taking 49 (14d6) fire damage on a failure or half damage on a success.